The myelodysplastic syndromes (MDS) are a heterogenous group of disorders characterized by clonal expansion of hematopoietic cells. Cytopenias and transformation to acute myeloid leukemia are important sequelae of MDS. The genetic basis of these disorders is poorly understood. The longterm goal of this project is to identify and characterize new mutations that are important for MDS initiation and progression. We propose to conduct a large-scale study of the genomics of MDS, utilizing high-throughput resequencing and array-based comparative genomic hybridization to identify novel genetic changes in samples from patients with MDS. We have also produced a unique mouse model of alkylator-induced MDS that will complement the search for mutations that are important for human MDS. We have several key resources available that make this project feasible, including a bank of matched tumor and germline (skin) samples from MDS patients, a close collaboration with the Washington University Genome Sequencing Center, prevalidated primers for all the genes selected for resequencing, and custom-produced bacterial artificial chromosome (BAG) arrays representing the complete tiling paths for the mouse and human genomes. With these resources in hand, we propose the following specific aims: Specific Aim 1: We will utilize highthroughput DMA sequencing and comparative genomic hybridization to identify genetic changes in samples from patients with myelodysplastic syndromes. Specific Aim 2: We will utilize a mouse model of t-MDS to identify and characterize novel mutations associated with the development of myelodysplastic syndromes. These Aims are complementary and are structured to provide independent validation for the mutations we find. Although the goals of this project are primarily mutation discovery, we will utilize standard in vitro and in vivo assays to confirm the biological consequences of the mutations we discover. All genetic data that we obtain in these studies will be deposited in publicly accessible databases in a format that will be useful to other investigators. Lay Audience Summary: We propose to use several unique resources available at our institution to discover new information about the genetic basis of the myelodysplastic syndromes. These findings should improve our ability to predict the prognosis of patients with MDS and provide a rational basis for designing specific therapies that are more effective and less toxic.